Park-steering assistance systems belong to a group of driver assistance systems that are increasingly used in vehicles in order to increase convenience and/or improve safety. The simplest driver assistance systems are for example an anti-lock braking system (ABS system), which prevents vehicle wheels from locking when braking. Other driver assistance systems include, for example, an electronic stability program (ESP system), which specifically brakes individual wheels in critical driving situations so as to maintain a vehicle's tracking, i.e. to prevent the vehicle from swerving.
Park-steering assistance systems are also among the driver assistance systems increasingly used in motor vehicles. In a simple arrangement, a park-steering assistance system ensures that the surroundings of the vehicle are searched with the aid of sensors for obstacles and/or free spaces. Preferably a surroundings map is produced that indicates on a display device obstacles and free areas in the surroundings of the vehicle. In a particularly simple arrangement, the representation takes the form of several light-emitting elements that represent a distance of the vehicle from an obstacle.
If the vehicle proceeds past a specified limit distance, a haptic, acoustic and/or visual warning is issued to the driver. More highly developed park-steering assistance systems are able to detect and measure parking spaces automatically, calculate a trajectory for the vehicle to follow into the ascertained parking space, and even drive the vehicle automatically into the parking space.
PCT International Published Patent Application No. WO 2005/100134 describes such a park-steering assistance system which provides for the park-steering assistance system to be deactivated if a safety check has determined that a parking process cannot be performed safely. The safety check verifies among other things whether the park-steering assistance system works correctly, i.e. does not issue an error message, whether a steering actuator works correctly, i.e. does not report an error, whether the communication system between the park-steering assistance system and the steering actuator works correctly, i.e. does not reveal an error, and whether an automatic steering intervention is requested.
European Published Patent Application No. 1 626 383 describes a method and a device for supporting a maneuvering of a motor vehicle. The device and method are provided in order to increase convenience and safety when a vehicle slowly approaches an obstacle, as occurs for example when parking. This is achieved by providing for the clutch to be opened at least partially in a maneuvering mode if a specified distance between the motor vehicle and an obstacle is undershot. The event of a vehicle velocity falling below a specified entry limit velocity combined with an accelerator pedal angle smaller than a specified entry limit angle is provided as an entry criterion that effects an automatic activation of the maneuvering mode.
Conventional park-steering assistance systems of the type mentioned at the outset provide for the park-steering assistance system to be capable of being activated via an operation of a control element. Since an accuracy, for example in measuring the surroundings for finding parking spaces, is a function of the vehicle velocity, conventional systems provide for the park-steering assistance system to be deactivated if a velocity value of the vehicle exceeds a first velocity threshold value. This arrangement is based on the assumption that, following the activation of the park-steering assistance system, a driver will approach a possible parking space with his vehicle at a relatively low vehicle velocity. In practice, the first velocity threshold value is usually fixed at 30 km/h.
If the vehicle velocity exceeds this first velocity threshold value, for example 30 km/h, then the park-steering assistance system is deactivated. Since there are situations in which a driver, without abandoning his search for a parking space or his intention to approach a parking space, must possibly increase his vehicle velocity to above 30 km/h, i.e. above the first velocity threshold value, it is unsatisfactory that he must manually reactivate the park-steering assistance system after having lowered the vehicle velocity again below the first velocity threshold value.